Position oven rack in lower-third of oven and preheat oven to 425°F. Spray an 8-inch square baking pan with cooking spray.
In a large mixing bowl, stir together the peaches, blueberries, and sugar. Set aside for 30 minutes. Drain fruit in a colander set over a bowl. Reserve 1/4 cup of juices (only 2 Tbs. if using frozen fruit). Transfer fruit to a large mixing bowl.
In small mixing bowl, whisk together the reserved juice, cornstarch, lemon juice, vanilla, cinnamon, nutmeg and pinch of salt. Pour over the fruit filling and gently stir together.
Pour filling into prepared pan and bake for 10 minutes until bubbly. If using frozen fruit, you will need to bake for additional time (up to 15 minutes more).
In another large bowl, whisk together cobbler topping dry ingredients: flour, sugar, baking powder, baking soda, and salt. Use a pastry blender, 2 forks, or your fingertips, cut in cold butter until mixture is pea-sized.
Stir in cold yogurt, stirring just until combined. You can add an additional tablespoon of yogurt if the topping is dry. Scoop six portions or spoon mixture on top of fruit mixture making sure the biscuit portions don't touch to ensure even baking.
Sprinkle on additional sugar.
Bake cobbler until topping is golden brown and filling is bubbly, 16-18 minutes, Let stand for 10 minutes before serving, serve with ice-cream.